PROJECT SUMMARY Aversive environmental events influence the daily lives of all people by altering their emotional states, decision making, and motivated behavior. For individuals with substance abuse disorders who are attempting to remain abstinent, these unfortunate events are clinically relevent, as they are frequently cited as a principle cause of relapse. In order to develop strategies to protect against this important determinant of relapse, it is essential to characterize the mechanisms through which aversive stimuli influence motivational neural circuitry. To this end, several decades of research have identified the nucleus accumbens (NAc) as a critical limbic/motor interface, heavily regulated by dopamine, where affective and associative reward information directly influence behavioral output. Unfortunately, the manner by which aversive stimuli regulate dopamine signaling remains poorly understood, with several studies producing conflicting results. We have identified an aversion signal, initiated by aversion-induced reductions in dopamine concentration, that is associated with increased striatal activity and drug seeking. The objective of this proposal is to determine how aversive stimuli regulate NAc dopamine signaling and the mechanisms through which reductions in dopamine alter neuronal activity in the NAc to shape behavior. To accomplish this objective, the proposal brings together a multi-disciplinary team that will use in vivo fast scan cyclic voltammetry, in vivo electrophysiology, and ex vivo slice electrophysiology to examine the independent contributions of reduced dopamine signaling and increased striatal activity to a panel of aversion- related behaviors, including drug seeking, and both reward and punishment sensitivity. In Aim 1 we will test the hypothesis that aversive stimuli, via reductions in NAc dopamine activate a subpopulation of aversion-responsive D2-like receptor-expressing NAc neurons to produce aversion-related behavioral responses. In Aim 2 we test the hypothesis that aversive stimuli increase corticotropin releasing factor (CRF) in the ventral tegmental area (VTA) and reduce dopamine in the NAc through a CRFR1- and GABAB receptor-dependent regulation of Girk channels on VTA DA neurons that project to the NAc shell. In Aim 3 we will examine upstream pathways that mediate the effects of aversive stimuli on NAc dopamine and behavior and will test the hypothesis that a beta adrenergic receptor-regulated pathway from the ventral bed nucleus of the stria terminalis to the VTA represents one such pathway. Understanding how aversive stimuli alter NAc dopamine signaling and how such alterations encode behavior has implications for understanding and treating a range of stress-related neuropsychiatric conditions including addiction and depression.